Looks like if I put a dummy variable inside the run method, like below:
public void run()
{
//PTW.print(firstName, lastName);
PrintTwoString ptws = new PrintTwoString(firstName, lastName);
synchronized (dummy) {
ptws.print();
}
//ptws.print();
}
Then I can comment out the synchronized block and remove the static word
there.
void print()
{
System.out.print(a + " " );
try
{
Thread.sleep((long)(Math.random() * 1000));
}
catch(InterruptedException ie)
{
}
System.out.println(b);
}
Then the output looks good.
A B
E F
C D
The question is why synchronized a dummy variable here works but not
synchronized just print method there? I appreciate if someone can help me
to understand this. Thx.
Lawrence Louie
On Thu, Feb 17, 2011 at 4:54 PM, Lawrence Louie <lawrence.lo...@gmail.com>wrote:
> Hi,
>
> I am having a question about the SynchronizedExample1 lab. If I am
> not using the static method to do the print, instead, I have a
> PrintTwoString print method(), the output does not look correct even
> this print method is synchronized. Can you help me to understand why
> this is the case? If I use the static method, then this code is
> synchronized, and the output looks correct. Thanks!
>
> The following is the output:
> A C E B
> F
> D
>
> Code:
> public class SyncThreadExample {
>
> /**
> * @param args
> */
> public static void main(String[] args) {
> // TODO Auto-generated method stub
> SyncThreadExampleHelper sth1 = new
> SyncThreadExampleHelper("A",
> "B");
> SyncThreadExampleHelper sth2 = new
> SyncThreadExampleHelper("C",
> "D");
> SyncThreadExampleHelper sth3 = new
> SyncThreadExampleHelper("E",
> "F");
>
> //sth1.print();
> }
>
> }
>
>
> public class SyncThreadExampleHelper extends Thread {
>
> private String firstName;
> private String lastName;
>
> public SyncThreadExampleHelper(String firstName, String lastName) {
> super();
> this.firstName = firstName;
> this.lastName = lastName;
> start();
> }
>
> public void run()
> {
> //PTW.print(firstName, lastName);
> PrintTwoString ptws = new PrintTwoString(firstName,
> lastName);
> ptws.print();
> }
> }
>
>
>
> public class PrintTwoString {
>
> PrintTwoString(String a, String b)
> {
> this.a = a;
> this.b = b;
>
> }
> synchronized void print()
> {
> System.out.print(a + " " );
> try
> {
> Thread.sleep((long)(Math.random() * 1000));
> }
> catch(InterruptedException ie)
> {
>
> }
> System.out.println(b);
> }
>
> private String a;
> private String b;
> }
>
> Lawrence Louie
>
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